On the multiplicity of the hyperelliptic integrals

Let $I(t)= \oint_{\delta(t)} \omega$ be an Abelian integral, where $H=y^2-x^{n+1}+P(x)$ is a hyperelliptic polynomial of Morse type, $\delta(t)$ a horizontal family of cycles in the curves $\{H=t\}$, and $\omega$ a polynomial 1-form in the variables $x$ and $y$. We provide an upper bound on the multiplicity of $I(t)$, away from the critical values of $H$. Namely: $ord\ I(t) \leq n-1+\frac{n(n-1)}{2}$if$\deg \omega <\deg H=n+1$. The reasoning goes as follows: we consider the analytic curve parameterized by the integrals along$\delta(t)$of the$n$``Petrov'' forms of$H$(polynomial 1-forms that freely generate the module of relative cohomology of$H$), and interpret the multiplicity of$I(t)$as the order of contact of$\gamma(t)$and a linear hyperplane of$\textbf C^ n$. Using the Picard-Fuchs system satisfied by$\gamma(t)$, we establish an algebraic identity involving the wronskian determinant of the integrals of the original form$\omega$along a basis of the homology of the generic fiber of$H$. The latter wronskian is analyzed through this identity, which yields the estimate on the multiplicity of$I(t)$. Still, in some cases, related to the geometry at infinity of the curves$\{H=t\} \subseteq \textbf C^2$, the wronskian occurs to be zero identically. In this alternative we show how to adapt the argument to a system of smaller rank, and get a nontrivial wronskian. For a form$\omega$of arbitrary degree, we are led to estimating the order of contact between$\gamma(t)$and a suitable algebraic hypersurface in$\textbf C^{n+1}$. We observe that$ord I(t)$grows like an affine function with respect to$\deg \omega$.Comment: 18 page

On the Wallman-Frink compactification of 0-dimensional spaces and shape

Here SF denotes the category whose objects are the pairs (X,P)where P is a metrizable ANR-space and X is a closed subset of P, and the morphisms between two objects (X,P) and (Y,Q) are the homotopy classes of mutations f:U(X,P)→V(Y,Q) (where U(X,P) and V(Y,Q) are the complete open neighborhood systems of X in P and Y in Q respectively). So two objects of SF are isomorphic if and only if they have the same shape in the sense of Fox (or Marde sic). The author constructs a covariant functor T from SF to the category C0 of all compact 0-dimensional spaces and continuous maps. This functor allows him to obtain new shape invariants in the class of metrizable spaces. Using this functor T he also constructs new contravariant functors to the the category of metrizable spaces and continuous maps and to the category of groups and homomorphisms. In order to construct T he uses the space of quasicomponents QX of a metrizable space X . Actually he uses the 0-dimensional compactification β0(QX) of QX. The space β0(QX) can be viewed as the 0-dimensional analogue of the Stone-Cech compactification. As a theorem he proves that two 0-dimensional metrizable spaces are of the same shape if and only if they are homeomorphic. This is a generalization in the metric case of a similar result for paracompacta due to G. Kozlowski and the reviewer [Fund. Math. 83 (1974), no. 2, 151-154] because there are metrizable spaces X such that ind(X)=0 but the covering dimension dim(X)>0